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<H1>viewable(?ViewableName)</H1>
Test/enumerate names of all existent viewables.
<DL>
<DT><EM>ViewableName</EM></DT>
<DD>Atom or string: name of a viewable.
</DD>
</DL>
<H2>Description</H2>


        <p><B>NOTE:</B>When there are no registered visualisation clients,
        this predicate fails with all arguments, and has no effect.</P>


       If <em>ViewableName</em> is instantiated, tests whether
       <em>ViewableName</em> is the name of an existent viewable. If not,
       <em>ViewableName</em> is successively instantiated to the names of all
       existent viewables.
<H3>Fail Conditions</H3>
Fails if ViewableName is not / cannot be instantiated to the name of an existent viewable.
<H3>Resatisfiable</H3>
yes
<H3>Exceptions</H3>
<DL>
<DT><EM>(4) instantiation fault </EM>
<DD>ViewableName is not an atom, string or free variable
</DL>
<H2>Examples</H2>
<PRE>

[Assuming that at least one visualisation client is registered]

     Success:

     viewable_create(my_viewable, [X,Y,Z], array([fixed], any)), 
       viewable(my_viewable).


     Failure:

     viewable(non_viewable)


     Exception raised:

     viewable(123).
     [raises error 4].
</PRE>
<H2>See Also</H2>
<A HREF="../../lib/viewable/viewable_create-2.html">viewable_create / 2</A>, <A HREF="../../lib/viewable/viewable_create-3.html">viewable_create / 3</A>
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